I have found out a few things, but still dont have the full picture.

1. I think it might have something with virtuemart. I had it installed for testing but I have removed it already, however the path that is in the error message. "/home/content/20/11104520/" is the same that was suggested by virtuemart to create it on the hosting as a safety path. Not sure where would be the error

2. If I change the default template to beez2 I can at least open the category and if I try to add an ad from there it works and I can save it, however if I want to update the same add to change the category the error message comes back.

HI I did some more research and indeed Joomfish and the multilingual site is creating the issue.

What I have experienced: When I want to create a new ad it takes me to category selection, however when I select the new category it redirects me to this link: /index.php?option=com_adsmanager&task=write&Itemid=197&lang=hu&catid=1 and here the error message is being displayed, but if I delete lang=hu from the link ex: see below

/index.php?option=com_adsmanager&task=write&Itemid=197&lang=hu&catid=1

I'm being redirected to this link index.php?option=com_adsmanager&task=write&Itemid=197&catid=1&lang=hu

and this one works correctly.

Anyone knows how can I manage to get to the link that works if I'm selecting a category?